The present invention is directed to alkaline aqueous development solutions for use in developing photo-resists.
Photo-resists are used to image patterns in a wide variety of applications such as printed circuit boards. In the case of printed circuit boards, the photo-resist is blanket coated or laminated to a copper clad core such that the photo-resist initially covers the copper. The photo-resist works by selectively exposing certain areas of the photo-resist to light, usually ultraviolet light, in the image of the desired pattern, thereby generating areas of photo-resist exposed to light and areas not exposed to light. The areas of the photo-resist exposed to light cross-link or polymerize thereby making those areas less soluble in the subsequent developer solution.
The exposed photo-resist is then exposed to a developer solution which will dissolve or strip the unexposed areas of the photo-resist but leave in tact the exposed areas of the photo-resist. For many photo-resists, the developer solution comprises a mildly alkaline aqueous solution which can be as simple as an aqueous solution of sodium or potassium carbonate (typically about 1% by weight). The optimum developer solution will effectively dissolve or strip all of the unexposed photo-resist areas from the substrate but leave all of the exposed areas of photo-resist fully in tact on the substrate and will accomplish this in a quick manner. This ideal development will thus leave portions of the substrate uncovered for subsequent treatment but other areas of the substrate covered to protect them from subsequent treatment.
Problems can occur in this development process if the developer solution (i) fails to completely remove all of the unexposed photo-resist, (ii) leaves residue on, or fails to leave clean, the substrate under the unexposed photo-resist and/or (iii) allows photo-resist residues to redeposit on areas of the substrate under the unexposed photo-resist. If any of the foregoing conditions exist, then the subsequent processing, intended to act selectively upon the areas of the substrate that were (previously) covered by now stripped unexposed photo-resist, will be ineffective or interfered with. Thus it is critical that the developer solution effectively strip all of the unexposed photo-resist leaving clean areas of substrate behind.
It is an object of this invention to disclose an improved developer solution for photo-resists that will more effectively strip all of the unexposed photo-resist from substrates and leave behind clean areas of substrate that are properly prepared for subsequent processing.